POSTIRRADIATION BLADDER DYSFUNCTION - DEVELOPMENT OF A RAT MODEL

The aim of this research was to establish a small animal model for the functional and morphological study of post-irradiation bladder dysfun ction. Young adult female Wistar rats were X-irradiated with single do ses of 10, 15, 20 or 25 Gy. Filling cystometry was performed to assess changes in reservoir function: the volume infused to produce a rise i n intravesical pressure of 5 cmH2O was calculated as an index of compl iance. A biphasic reduction in this index was noted in animals receivi ng 15-25 Gy; the first reduction developed at about 4 weeks, and the s econd started at 3-4 months and persisted at 6 months. Bladder tissue was taken at this time (6 months post-irradiation) for morphological s tudy. Histological examination demonstrated an increased mast cell den sity in the irradiated bladders, but was otherwise non-specific; fibro sis was discernible in only half of the 18 animals studied. Electron m icroscopy showed focal degeneration of smooth muscle cells, and in som e areas there was selective degeneration of unmyelinated axon profiles . The biphasic reduction in the compliance index is consistent with th e timing of the symptoms of the acute and late irradiation reactions r eported by radiotherapy patients. Changes in axon profiles and mast ce ll density may be of functional significance.